As nations become more industrialized and the world more populated, there is a constant increase both in the demand for electricity and in the generation of waste.
Electrical energy today is typically generated by power plants that burn fossil fuels such as coal, natural gas or heavy diesel oil to generate electricity. Such plants, however, also generate significant air pollution. Nuclear power plants produce electricity more cleanly, but they are being phased out worldwide due to popular concern over their perceived risks and the radioactive nature of the waste they generate. In view of the increasing costs and dwindling supply of fossil fuels, many countries are recognizing and encouraging the production of electrical energy from renewable sources of fuel, such as wind, solar, hydro and waste/biomass.
Waste (including MSW, industrial waste, toxic waste, and coal ash and fines) is currently being dumped into polluting landfills or being burned in common incinerators, creating emissions of pollutants, including carcinogenic materials such as semi-volatile organic compounds (SVOCs)—dioxins, furans, etc.—that are products of low temperature combustion.
Landfills are becoming full, and the availability of new sites near heavily populated areas is limited worldwide. Additionally, the continued pollution of ground water by hazardous leachate, as well as health concerns caused by malodor, rodents and fumes, have rendered landfills undesirable. These issues and others have resulted in the development of the NIMBY Syndrome (“not in my backyard”) in most populations. For these reasons, the European Union is forcing closure of all landfills by the year 2002 and mandating that existing landfills meet new, more stringent leachate and pollution control standards, thus increasing the costs of landfills markedly.
Incinerators also have been closed down or banned in many countries because of hazardous air emissions and resulting ash production. As a result of the low temperature combustion that takes place in these incinerators, hydrocarbon chains are not completely severed and are released into the atmosphere as SVOCs, which are known carcinogens and are passed through to humans via the food chain, for example, as dioxins that are deposited on grass and eaten by cattle and end up in milk sold to humans. The fixed carbons in the waste also are untouched by the low temperature incineration process and end up as bottom ash and fly ash. This ash makes up almost 25% of the waste and is considered hazardous due to its leachability once land-filled. Many countries are now prohibiting the direct landfill of ash.
There thus exists a need both for a source of readily renewable electrical energy, and for an apparatus and process for dispensing with various forms of waste, that solve the foregoing problems. This need has been met in part by the apparatus and process disclosed and claimed in U.S. Pat. Nos. 5,544,597 and 5,634,414 issued to Camacho and currently assigned to Global Plasma Systems Group, Inc. (the “Camacho Patents”). The Camacho Patents disclose a system in which waste is compacted to remove air and water and delivered in successive quantities to a reactor having a hearth. A plasma torch is then used as a heat source to pyrolyze organic waste components, while inorganic waste components are removed as vitrified slag.
There remain, however, several disadvantages to, or problems not solved by, the apparatus and process disclosed and claimed in the Camacho patents. First, the introduction of waste into the reactor from a single direction can lead to an uneven build-up of material on one side of the reactor, causing channeling and bridging. Channeling is the uneven distribution of gas flow up through the waste bed that in turn creates an uneven heating of the waste bed. This creates pockets of un-gasified waste that decreases the overall efficiency of the process. Bridging is the binding together of portions of the waste bed into a solid mass that blocks the upward flow of gas and the downward flow of waste in that portion of the reactor. This also decreases the efficiency of the process and can increase the degradation of the refractory material lining the reactor. Second, the bottom of the reactor does not always distribute heat evenly throughout the bed of waste introduced in the reactor. Third, the single plasma torch used in the Camacho patents is sometimes not enough to provide sufficient heating. Fourth, it would be desirable to increase the number of gas inlet valves and improve their location to introduce desired gases more efficiently to the reaction. Finally, the apparatus used in the Camacho Patents for compacting waste requires that the waste first be separated from its containers, leading to reduced efficiency and increased cost.
It is therefore the overall object of the present inventors to disclose an improvement of the previously disclosed apparatus and process for the pyrolysis, gasification and vitrification of organic material, such as waste.
It is a further object of this invention to provide an improved material feeding system in order to enhance further the efficiency of the process as well as to increase the flexibility of the system, increase the ease of use of the material handling system, and allow the reactor to receive a more diverse and varied material stream.
It is an additional object of this invention to provide an improved design of the apparatus to enhance the process control of the gasification of the material, allow the gasification process to occur in the reactor, ensure optimum performance, ensure complete breakdown of all hydrocarbon chains fed into the system, decrease wear and tear in the refractory, and decrease torch power consumption and optimize energy performance of the entire process.
It is a further object of this invention to provide an improved method of handling hot exit gas and better preparing it to meet the requirement of a gas turbine prior to feeding it into an integrated combine cycle gas turbine system.
It is also an object of this invention to disclose the plasma pyrolysis, gasification and vitrification (PPGV) process of mixed sources of waste as a safe and efficient method of producing a fuel gas for feeding into a combined cycle gas turbine to produce renewable electrical energy.
Finally, it is an object of this invention to disclose the utilization of the PPGV process of organic material to produce H2 gas as a fuel source for a fuel cell system.
Other objects and advantages will be more fully apparent from the following disclosure and appended claims.